Study RIT-II-001 is a phase II, multicenter study of the safety, tumor and organ dosimetry, dosimetry methods, and efficacy of Iodine-131 Anti-B1 Antibody for the treatment of patients with low-grade or transformed low-grade non-Hodgkin's lymphoma (NHL). The primary objective of this study is to demonstrate that each site could accurately conduct the whole body dosimetry required for the safe and effective dosing of Iodine-131 Anti-B1 Antibody. Additional objectives of this study are to evaluate the efficacy, dosimetry, and safety of Iodine-131 Anti-B1 Antibody.